In general, not only in the field of electronic devices, but also in the field of digital devices such as mobile telephones, the electromagnetic shielding technique is required for suppressing adverse effects from electromagnetic waves exerted internally as well as externally.
The cabinet structure in an electronic device is generally formed by machining a plurality of metal plate members into constituent elements of a cabinet and connecting edge portions of the plate members in the butted state through screws, etc.
In such a cabinet structure, when there is any gap in the joint between the metal plate members, electromagnetic waves, generated from electronic parts installed in the cabinet, tend to leak outside through the gap, and external electromagnetic waves tend to invade into the cabinet through the gap.
For this reason, in order to eliminate such a gap, it is necessary to machine the edge portions of the respective plate members to completely plane faces and to make the edge portions in closely contact with each other so as to be connected.
However, it is technically difficult to machine the edge portions to completely flat faces. Moreover, even when such plate faces are provided through machining, the edge portion tends to be deformed due to fastening process of screws, etc. Therefore, with respect to the cabinet, normally, the gaps tend to exist although there are variations in the degree thereof.
Here, a technique for placing electromagnetic wave shielding plates in the joints of the plate members in order to prevent invasion and leakage of electromagnetic waves to and from the cabinet has been well known.
With respect to such an electromagnetic wave shielding plate, an expensive material such as phosphor bronze is used, resulting in an increase in the material costs. Moreover, since the electromagnetic wave shielding plates are provided as separated components from the cabinet, the operation for attaching these to the above-mentioned gaps is required, resulting in an increase in the assembling costs of the cabinet.
Furthermore, due to the difference in materials of the plate members and the magnetic wave shielding plates that constitute the cabinet, a contact electrical potential difference occurs due to contact between different kinds of metals. In the case when the state having this contact electrical potential difference continues for a long time, rust portion is generated due to an oxidation-reduction reaction. This rust portion forms a portion in which the electrical conductivity of the contact between the plate members and the electromagnetic wave shielding plates is lowered, that is, an insulating portion, resulting in the same situation as the occurrence of the above-mentioned gap. As a result, there is a reduction in the electromagnetic wave shielding effects by the electromagnetic wave shielding plates.
In a cabinet structure of an electronic device, an objective of the present invention is to provide a cabinet structure which can reduce the above-mentioned costs, and also maintain the electromagnetic wave shielding function continuously for a long time.